SkImage_Raster's pixels are always immutable.

src/core/SkPixelRef.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapCache.h"
 #include "SkMutex.h"
 #include "SkPixelRef.h"
@@ skipping 88 matching lines @@
 #endif
 
 {
 #ifdef SK_TRACE_PIXELREF_LIFETIME
     SkDebugf(" pixelref %d\n", sk_atomic_inc(&gInstCounter));
 #endif
     this->setMutex(NULL);
     fRec.zero();
     fLockCount = 0;
     this->needsNewGenID();
-    fIsImmutable = false;
+    fMutability = kMutable;
     fPreLocked = false;
     fAddedToCache.store(false);
 }
 
 
 SkPixelRef::SkPixelRef(const SkImageInfo& info, SkBaseMutex* mutex)
     : fInfo(validate_info(info))
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
     , fStableID(next_gen_id())
 #endif
 {
 #ifdef SK_TRACE_PIXELREF_LIFETIME
     SkDebugf(" pixelref %d\n", sk_atomic_inc(&gInstCounter));
 #endif
     this->setMutex(mutex);
     fRec.zero();
     fLockCount = 0;
     this->needsNewGenID();
-    fIsImmutable = false;
+    fMutability = kMutable;
     fPreLocked = false;
     fAddedToCache.store(false);
 }
 
 SkPixelRef::~SkPixelRef() {
 #ifndef SK_SUPPORT_LEGACY_UNBALANCED_PIXELREF_LOCKCOUNT
     SkASSERT(SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount || 0 == fLockCount);
 #endif
 
 #ifdef SK_TRACE_PIXELREF_LIFETIME
@@ skipping 195 matching lines @@
             SkNotifyBitmapGenIDIsStale(this->getGenerationID());
             fAddedToCache.store(false);
         }
     }
     // Listeners get at most one shot, so whether these triggered or not, blow them away.
     fGenIDChangeListeners.deleteAll();
 }
 
 void SkPixelRef::notifyPixelsChanged() {
 #ifdef SK_DEBUG
-    if (fIsImmutable) {
+    if (this->isImmutable()) {
         SkDebugf("========== notifyPixelsChanged called on immutable pixelref");
     }
 #endif
     this->callGenIDChangeListeners();
     this->needsNewGenID();
     this->onNotifyPixelsChanged();
 }
 
 void SkPixelRef::changeAlphaType(SkAlphaType at) {
     *const_cast<SkImageInfo*>(&fInfo) = fInfo.makeAlphaType(at);
 }
 
 void SkPixelRef::setImmutable() {
-    fIsImmutable = true;
+    fMutability = kImmutable;
+}
+void SkPixelRef::setTemporarilyImmutable() {
+    SkASSERT(fMutability != kImmutable);
+    fMutability = kTemporarilyImmutable;
+}
+
+void SkPixelRef::restoreMutability() {
+    SkASSERT(fMutability != kImmutable);
+    fMutability = kMutable;

[robertphillips, 2015/07/29 19:26:29]

Hmmm .. can we get rid of the 'notifyPixelsChanged' ?

+    this->notifyPixelsChanged();  // This is just precautionary.
 }
 
 bool SkPixelRef::readPixels(SkBitmap* dst, const SkIRect* subset) {
     return this->onReadPixels(dst, subset);
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 bool SkPixelRef::onReadPixels(SkBitmap* dst, const SkIRect* subset) {
     return false;
@@ skipping 26 matching lines @@
     }
 
     result->fUnlockProc = unlock_legacy_result;
     result->fUnlockContext = SkRef(this);   // this is balanced in our fUnlockProc
     result->fCTable = fRec.fColorTable;
     result->fPixels = fRec.fPixels;
     result->fRowBytes = fRec.fRowBytes;
     result->fSize.set(fInfo.width(), fInfo.height());
     return true;
 }